Powder flow detection

ABSTRACT

Apparatus for detecting powder flow along a powder flow path includes a light source and a light detector for detecting light from the light source directed across the powder flow path as powder flows through said powder flow path. A circuit receives the output from the light detector and determines an average or RMS of the signal received by the light detector. The circuit may determine whether there is flow or no flow of powder or whether there is a change in flow rate of powder. Preferably, the apparatus is used in combination with a dense phase powder pump, which causes the powder to flow in pulses from the pump outlet into the powder flow path. More preferably, the light source and detector are enclosed in a housing that is connected between the pump outlet and a powder feed hose which supplies powder to a spray gun or hopper.

TECHNICAL FIELD OF THE DISCLOSURE

The disclosure relates generally to detecting whether powder coatingmaterial is flowing through a tube. More particularly, the disclosurerelates to detecting powder coating material flow for flow/no flowconditions and optionally to detect changes in flow rate.

BACKGROUND OF THE DISCLOSURE

Powder coating materials are commonly applied to objects or workpiecesusing well known spraying technologies. These technologies may includeelectrostatic and non-electrostatic processes as are well known. Also,some powder coating material application systems deliver powder coatingmaterial to a spray gun or other application device in dilute phase, oralternatively in dense phase, as is well known in the art.

SUMMARY OF THE INVENTIONS

In accordance with one aspect of the one or more inventions disclosedherein, a powder coating material flow detection concept uses lightenergy to detect the presence or absence of powder flow within a tubularmember. The intensity of light that is transmitted through the tubularmember is related to whether powder coating material is present. In aparticular embodiment, a circuit receives a signal related to theintensity of light that passes through the tubular member and determineswhether there is powder flow. In a more specific embodiment, a lightdetector produces an output in response to intensity of light thatpasses through the tubular member, and a circuit determines an averagevalue of the output. The circuit can then determine whether there ispowder flow based on the average signal.

In another aspect of one or more of the inventions disclosed herein, thecircuit determines an average value of the light intensity that passesthrough the tubular member and from that average the circuit determinesa characteristic of powder flowing through the tubular member. In oneembodiment, the characteristic may be a flow/no flow determination. Inan alternative embodiment, the characteristic may be whether flow ratehas changed.

In the various embodiments, the average calculation may be an RMScalculation for example, or other calculation as required.

In one embodiment, the light source and detector are enclosed in ahousing that is connected to the pump outlet between the pump outlet anda powder feed hose, wherein a powder feed hose supplies powder to apowder hopper or a spray gun.

These and other aspects and advantages of the one or more inventionswill be readily understood and appreciated from the following detaileddescription hereinafter and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematic of a powder coating materialapplication system that uses an embodiment of one or more of theinventions disclosed herein;

FIG. 2 is an enlarged view of the sensing function embodiment of FIG. 1;

FIG. 2A is an alternative embodiment of the sensing function of FIG. 2shown in phantom in FIG. 2, shown in side elevation;

FIG. 3 is an embodiment of a response function of FIG. 1;

FIGS. 4A-4E illustrate an exemplary output signal from a light detectorfor different powder flow conditions, with the single waveform shown ina simplified manner for ease of understanding;

FIG. 5 is an elevation of a dense phase pump with an embodiment of oneor more of the inventions disclosed herein;

FIG. 6 is a longitudinal cross-section of FIG. 5 taken on the line 6-6of FIG. 5; and

FIG. 7 is the longitudinal cross-section of FIG. 6 rotate 90 degrees.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Although the exemplary embodiments are described herein and presented inthe context of specific examples of components and parts and functions,those skilled in the art will readily appreciate that many differenttypes of designs and alternative configurations may be used as neededfor a particular application. For example, many different powder pumpdesigns may be used, as well as many different choices of material aswell as form, fit and function for the tubular member that is in fluidcommunication with an outlet of the powder pump and that contains thepowder flow. We use the terms “tubular member” and “tube”interchangeably to refer to any conduit or passageway that contains aflow of powder. While the exemplary embodiments refer to common flexiblecylindrical tubing, such is not required, and the tube or tubing maytake on any suitable geometry and characteristics, and may include anypassageway through which powder flows (for example, a block or otherstructure may be used that has an internal passageway through whichpowder travels). A feature of interest is that the tube or passagewayincludes at least a portion that can admit electromagnetic energythrough a wall that defines the sensing portion of a passageway or tube.We use the term “sensing function” to refer to an arrangement orstructure that detects a characteristic of powder flow. In the exemplaryembodiments, the sensing function may be realized in the form of asource and detector of electromagnetic energy. The inventions are notlimited to any particular frequency or wavelength of electromagneticenergy, with the only feature of interest being that the selectedelectromagnetic energy includes one or more wavelengths that can passthrough the tube or passageway wall and be detected by a suitable lightdetection device. We therefore also refer herein to the electromagneticenergy generically as light energy regardless of the selected wavelengthor plurality of wavelengths. The tube or passageway wall need not befully transparent to the selected electromagnetic energy but rather ispreferably sufficiently transparent so that light intensity for lightthat passes through the tube or passageway wall can be related towhether powder is flowing through the passageway or tube and in someembodiments whether the flow rate has changed. The inventions are notrestricted to any particular spraying technology, and may be used withcorona, tribo-electric and non-electrostatic spraying technologies. Theinventions may also be used with many different types of spray guns orother powder coating material application devices, including manualspray guns and automatic spray guns. Many different control systems forthe pumps, spray guns and other system components may be used. Except asotherwise may be noted, the size, materials, layout and structuralaspects of the various disclosed components are design options. Thepowder coating material application system may utilize a wide variety ofsystem features including a feed center for supplying powder coatingmaterial, spray guns, electronic control systems for the spray booth,spray guns, gun control systems, gun movers, reciprocators, oscillatorsand so on, overhead conveyor systems, and powder overspray recoverysystems.

In the exemplary embodiments, we determine an average value, for examplean RMS (Root Mean Square) value, of a time variant analog signalwaveform produced by a light detector. We therefore consider the term“average” herein to include, but not be limited to, an RMS calculation.Other mathematical calculations could alternatively be made to representone or more characteristics of the waveform as needed. For example, thewaveform could be digitized and analyzed in the frequency domain. Thefeature of interest is that the light detector output waveform isanalyzed so as to be able to identify changes in the detected lightintensity in order to determine whether powder is flowing in the sensingportion of the tubular member, or in another embodiment, identifychanges in the detected light intensity to determine whether flow ratehas changed. Because the light detector output is a time variant voltagesignal in the exemplary embodiment, the use of average value, such as anRMS value for example, is a convenient but not required method toidentify such changes in the light intensity. The inventions are alsonot limited to the use of light detectors that produce an analog voltageoutput, but other detectors may be used as needed or convenientlyavailable, with appropriate changes in the circuit used for processingthe output signal.

The inventions also are not limited to use with any particular type ofpowder coating material and we therefore herein refer generically topowder which we intend to include any dry particular material, and inspecific exemplary embodiments, powder coating material. Moreover, thepowder may be used in dilute phase or dense phase and also may bedelivered with a continuous flow or pulsed flow.

While various inventive aspects, concepts and features of the inventionsmay be described and illustrated herein as embodied in combination inthe exemplary embodiments, these various aspects, concepts and featuresmay be used in many alternative embodiments, either individually or invarious combinations and sub-combinations thereof. Unless expresslyexcluded herein all such combinations and sub-combinations are intendedto be within the scope of the present inventions. Still further, whilevarious alternative embodiments as to the various aspects, concepts andfeatures of the inventions—such as alternative materials, structures,configurations, methods, circuits, devices and components, alternativesas to form, fit and function, and so on—may be described herein, suchdescriptions are not intended to be a complete or exhaustive list ofavailable alternative embodiments, whether presently known or laterdeveloped. Those skilled in the art may readily adopt one or more of theinventive aspects, concepts or features into additional embodiments anduses within the scope of the present inventions even if such embodimentsare not expressly disclosed herein. Additionally, even though somefeatures, concepts or aspects of the inventions may be described hereinas being a preferred arrangement or method, such description is notintended to suggest that such feature is required or necessary unlessexpressly so stated. Still further, exemplary or representative valuesand ranges may be included to assist in understanding the presentdisclosure, however, such values and ranges are not to be construed in alimiting sense and are intended to be critical values or ranges only ifso expressly stated. Moreover, while various aspects, features andconcepts may be expressly identified herein as being inventive orforming part of an invention, such identification is not intended to beexclusive, but rather there may be inventive aspects, concepts andfeatures that are fully described herein without being expresslyidentified as such or as part of a specific invention, the inventionsinstead being set forth in the appended claims. Descriptions ofexemplary methods or processes are not limited to inclusion of all stepsas being required in all cases, nor is the order that the steps arepresented to be construed as required or necessary unless expressly sostated.

The exemplary embodiments disclose two basic configurations of theinventions and flow detection concepts disclosed herein. Both conceptsare based on method and apparatus to detect a characteristic of powderflow along a powder flow path with a sensing function that uses lightenergy. By “powder flow path” we mean an interior space for flow ofpowder through a containing structure such that the powder flows fromone point to another point. An example of a powder flow path thereforeis an interior space of a member through which powder flows, perhaps ahose or tube or any conduit, tubular member, or passageway that containsthe powder flow. The powder flow path of interest in the exemplaryembodiments is a sensing portion of the powder flow path within asensing portion of the containing structure or passageway. For example,in the exemplary embodiments herein, the sensing portion may be aportion of the powder flow path through which light energy passes so asto detect flow characteristics of the powder. The flow characteristicsmay include a no flow condition. Therefore, the light energy may betransmitted into the powder flow path through all or a sensing portionof a wall of the containing structure, or through a sensing portion ofan inner space delimited by the wall structure. In the exemplaryembodiments herein, light energy may be transmitted through a tube wallof a tubular member to pass into the powder flow path. As used herein, a“portion” of a tubular member refers to the sensing portion unlessotherwise noted (for example, reference is also made herein to a flaredportion as will be described below). In the first configuration, wedescribe method and apparatus for detecting a characteristic of powderflow in the form of detecting a flow or no flow condition by sensinglight energy. The detected condition, especially a no flow condition,may be used to alert an operator or in some other manner influence theoperation of the coating system so as to reduce or eliminate the wasteof uncoated or inadequately coated workpieces. In order to make the mostof this optional warning, we prefer, although it is not required, tolocate the sensing function in close proximity to an outlet of a powdercoating material pump.

In the second configuration, we describe method and apparatus fordetecting a change in flow rate of powder through a sensing portion of apowder flow path, for example within a tubular member, using lightenergy. The change in flow rate condition may include detection of a noflow condition, so the two basic concepts are not necessarily mutuallyexclusive of each other. The second configuration does not necessarilyrequire a determination of the actual flow rate, but rather we look forchanges in the flow rate. The second configuration, therefore, mayoptionally utilize a calibration feature as will be further explainedherein. For the second configuration, we also prefer but do not requireto locate the sensing function in close proximity to an outlet of apowder coating material pump.

For both concepts and configurations, we provide an optical sensingfunction by which we use light energy to detect powder flowing throughthe sensing portion of a tubular member or passageway. In a preferredalthough not necessarily required embodiment, we use an average or RMSvalue of a light energy sensor signal to detect powder flow. Thisaverage or RMS value allows us to adjust or calibrate for differentpowder materials that may exhibit different optical properties such astransmittance or reflectance. The use of average or RMS values alsoallows us to compensate or calibrate for optical properties fordifferent materials that may be used for the sensing portion of thetubular member or passageway.

FIG. 1 illustrates an embodiment of the concepts of one or more of thepresent inventions. A powder coating material application system 10 mayinclude a source 12 of powder coating material (hereinafter “powder”)such as a box, container, hopper, feed center or other receptacle as iswell known in the art. A pump 14 may be used to draw powder from thepowder supply 12 and push the powder through a feed hose 16 to an enduse 18, for example, a spray gun or, in the case of a bulk transferpump, or another receptacle.

In the example of FIG. 1, the pump 14 may be realized in the form of adense phase pump being of the type that pulls powder into a pump chamberusing negative pressure and pushes the powder out of the pump chamberunder positive pressure. The pump chamber typically is made of amaterial that is porous to air but not the powder media. Such a pumpuses less air in the air powder mixture as compared to a venturi pumpfor example, and therefore is referred to as a dense phase pump. Anexample of a dense phase pump is described in published United StatesPatent Application number 2005/0158187 A1, the entire disclosure ofwhich is fully incorporated herein by reference.

We do not describe in the detail the structure and operation of the pump14 as it is not necessary for understanding and practicing the presentinventions. However, the pump 14 will typically have an associated pumpcontrol function or circuit 20 which operates to adjust the powder flowrate control 22 which is the flow rate of powder that is output by thepump, typically stated in pounds per minute, for example. Alternatively,however, some pumps may operate simply in an ON/OFF manner. The flowrate control 22 may be used, for example, to set the output powder flowrate from the pump 14 anywhere from 0% to 100% of the maximum flow rateof the capability of the pump 14.

For a dense phase pump 14, the pump 14 may have an inlet 24 and anoutlet 26. The inlet 24 receives powder through a supply hose 28 that isin fluid communication with the powder supply 12. The outlet 26 of thepump 14 is in fluid communication with the feed hose 16. The pumpcontrol circuit 20 can control operation of the pump 14 through a seriesof valves such as a first valve 30 that controls flow of powder into thepump 14 and a second valve 32 that controls flow of powder out of thepump 14. These valves 30, 32 are operated in conjunction with the timingof the application of suction and pressure to the pump chamber (notshown). Accordingly, a dense phase pump 14 produces a powder flow at theoutlet 26 in the form of pulses or packets of powder. Additional orsecond inlet and outlet hoses 34, 36 respectively may be used for a pump14 design that may include to pump chambers that operate out of phasewith respect to each other, meaning that while one of the pump chambersis pulling in powder the other pump chamber is pushing powder out, andvice-versa. The use of multiple chambers can be used to increase flowrate of powder outputted from the pump. Additional control valves suchas a third valve 38 in the second inlet hose 34 and a fourth controlvalve in the second outlet hose 36 may be used by the pump controlfunction 20 to control overall timing of the pump to effect a desiredflow rate of powder at the pump outlet 26.

The information presented thus far about the operation of the densephase pump 14 is well known and explained in much more detail in theincorporated patents, and reference may be made thereto for suchexplanation. An important note though is that a dense phase pump willproduce an output powder flow that can be characterized as pulses ordiscrete slugs of dense phase powder.

With the above description of the pump 14 as the background for use ofthe inventive concepts herein, we also now refer to FIGS. 2 and 3 fordescription of an exemplary embodiment of an apparatus for detectingpowder flow. By detecting whether powder is flowing in a passageway,such as for example a passageway in communication with the end use 18,we can generate a warning or other alarm when the flow is unexpectedlyinterrupted, or alternatively when the flow rate changes. Thisnotification or alarm can then be used to inform an operator that thecoating process may not be correct, allowing the operator to takecorrective action if needed to minimize waste.

An apparatus 50 for detecting flow of powder in a passageway, such asthe tube 16 for example, may include in a basic form, a sensing function52 and a response function 54. In practice, the sensing function 52alone can produce an output signal that indicates or contains theinformation of whether powder is flowing. This output signal couldsimply be displayed on a scope without any signal processing for exampleand an operator could visually see the signal indicating powder flow orno flow. Or alternatively the output signal could directly drive a lampor other indication device to the operator as to the state of the outputsignal. In such a case, the scope or the indication device could serveas the response function 54. However, the raw data out from the sensingfunction in many cases will not be adequate to determine whether thereis powder flow because there is no reference for comparison. But in ourexemplary embodiment, we may use the response function 54 to perform ananalysis of the sensing function 52 output signal in order to furtherrefine its utility in indicating whether there is a flow or no flowcondition or alternatively whether flow rate has changed. In ourexemplary embodiment, the response function 54 may be realized in theform of a circuit (described below) that includes a signal processingcapability such as a microprocessor that receives the analog output fromthe light detector 58 and determines an average or RMS value of thatsignal over time.

In the exemplary embodiment of FIGS. 1-3 then, the sensing function 52uses optical properties of electromagnetic energy, herein referred to aslight energy, to detect powder flow in a passageway. Because the pumpoutlet 26 is connected to the feed hose 16 that feeds the spray gun orother end use, we find it desirable although not necessarily required tosense powder flow in the hose 16 in close proximity to the pump outlet26.

The sensing function 52 (see FIG. 2) may be realized in the form of alight source 56 and a light detector 58. The light source 56 and lightdetector 58 may be disposed as to be diametrically facing each other onopposite sides of the feed hose 16 to provide line of sight detection.This assures that the light energy passes through the center of the feedhose 16 where most of the powder can be expected to flow. Because theinventions have use in many different applications, from here on we willrefer to the hose 16 as providing a powder flow path 60, such aspassageway 60, through which powder flows, particularly a passageway 60provided by a tube or tubular member 62 (for example, the feed hose 16)keeping in mind that our use of the term tube or tubular member is notlimited to just flexible cylindrical members but can be any structurethat provides a passageway for the flow of powder, even a bore in ablock for example.

The basic concepts utilize the idea that when there is no powder in thepassageway 60, then a maximum intensity of light from the light source56 that travels through the passageway 60 via the tube 62 wall willreach the light detector 58. The light detector 58 will generate adetector output 64 that is related to the intensity of the light that isdetected. The intensity of light that reaches the light detector 58 willdepend on the intensity of the light that is produced by the lightsource 56, the transparency of the tubular member 62 and the efficiencyof the light detector 58 in converting the detected light intensity intoan output signal, for example, voltage or current. The transparencycharacteristic of the tube wall may be selected based on the wavelengthof light that is generated by the light source 56. An exemplary lightsource 56 is a red light emitting diode, for example, part no.WP7104SRC/D available from Kingbright, and a suitable light detector 58is a light to voltage converter such as a TSL12S available from TexasAdvanced Optoelectronic Solutions, Inc. Many alternative light sourcesand light detectors may be used. The light source 56 and light detector58 will be selected for compatibility and also with the transparency ofthe tubular member 62. The example light detector 58 produces nearly a 5volt DC output 64 at maximum intensity.

When powder is present in the tubular member 62 the powder will reflect,scatter, or absorb light energy or otherwise reduce the intensity of thelight that passes through to the light detector 58. Accordingly, theoutput signal 64 from the light detector 58 will change, in this casethe voltage will decrease. If all the light is blocked then the lightdetector output 64 will be near zero volts.

With a dense phase pump 14 as noted, the powder that flows from theoutlet 26 is pulsed. This will cause the light detector 58 to produce anoutput signal that is also pulsed. Typically we do not see the detectoroutput go to near zero when a powder pulse passes between the lightsource 56 and the light detector 58, but such could happen.

Because we are detecting powder flow through a tubular member 62, weprefer although it is not required in all cases, for the tubular member62 to be generally vertically oriented so that gravity can assist thepowder to clear the tube.

Not all feed hoses 16 or other tubular members providing the powder flowpassageway 60 are sufficiently transparent to light energy. Therefore,we contemplate that in some cases it will be desirable to provide asection or portion 66 of tube to provide the needed transparency for thelight energy. This portion 66 may be a piece of tube that is inserted inline with the feed hose 16 for example, again preferably in a locationthat is proximate the pump outlet 26. How the portion 66 is insertedinto the passageway so as to provide a portion of the passageway 60 is amatter of design choice, and we present one embodiment in FIGS. 5-7herein. For example, a suitably transparent portion may be spliced intothe main hose 16. In any case, the portion 66 of the tubular member 62through which light energy is transmitted, whether it is a continuoustube or an added piece, serves as the sensing portion 66 of the tubularmember or passageway 60 for detecting flow of powder therein.Preferably, the length to width ratio of the sensing portion 66 shouldbe great enough so that if there are any boundary layers where thesensing portion 66 is installed, that the boundary layer will not retainpowder within the path for the light energy to travel from the lightsource 56 to the light detector 58.

FIG. 4A shows in a simplified manner the output voltage from the lightdetector 58 versus time. FIG. 4A relates to a condition of no powderflow, so that the light detector output 64 is a maximum voltage that isabout the maximum voltage output 68 available from the detector 58. Theactual maximum output 64 for detected light energy will typically beslightly less than the maximum output available from the light detector58 because of some attenuation, deflection or diffraction of some of thelight intensity as the light energy passes through the wall material ofthe tubular member 62. The maximum voltage out 64 also is a function ofhow well the light source 56 is outputting light intensity. The signal64 is basically a steady state value because the light remainsuninterrupted. For all of the FIGS. 4A-4E we use simplifiedrepresentations of the output signal from the light detector 58 forclarity and ease of understanding. In practice, the analog output of thelight detector 58 will be a more jagged trace as the instantaneousoutput signal will fluctuate with the transmittance of the powder. So wesmooth out or stylize the waveform in order to more clearly set forththe operational principles.

FIG. 4B illustrates the output voltage from the light detector 58 forthe condition where there is a slug of powder between the light source56 and the light detector 58, or simply the sensing portion 66 of thetube 62 is basically filled with powder. In this condition, the powderbasically blocks most of the light energy from passing through thesensing portion 66 of the tube and the light detector output 64 is nearzero volts.

Now, as a practical matter, during normal use the powder will not simplysit in the sensing portion 66 and block all light to the light detector58. Rather, for a dense phase pump, the powder pulses will result in anaverage intensity of detected light over time for a given flow rate ofpowder from the pump 14. Therefore, we can use the light detector outputsignal 64 to indicate a flow or no flow condition by determining anaverage value of the output signal 64 and verifying that is fallssomewhere in between the two extremes of FIGS. 4A and 4B. For theexemplary embodiment of FIGS. 4C-4E we use RMS as the averagecalculation.

For example, FIG. 4C illustrates an example for a dense phase pump 14that is set to a flow rate of about 40% of the maximum output flow ratefor the pump 14. Each slug of powder causes a reduction in the intensityof the light that reaches the light detector 58, resulting in the pulsedoutput nature of the light detector signal 64. Each slug of powderblocks some of the light energy from reaching the light detector 58 andso the detector output 64 voltage drops as at 70. A repeating series ofthese drops occurs at intervals that correspond with the pulses ofpowder that are pushed out of the outlet 26 of the pump 14. Thus, thevalleys 70 represent the maximum drop in light intensity when the powderslug passes between the light source 56 and the light detector 58. Aseach slug clears through the sensing portion 66, then the voltage outputfrom the light detector 58 returns near its maximum as at 72. Thewaveform 64 is not a perfect square or rectangle because the slugs ofpowder do not typically have sharp leading and trailing edges.

Because the waveform produced by the light detector output 64 is analog,we can easily calculate the RMS value (V1) of that signal over time asindicated by the line 74. This value 74 will be generally steady so longas the amount of powder in each slug remains generally constant which istypical for a dense phase pump. Note than the RMS value of the outputsignal 64 from the light detector 58 directly corresponds to the RMSvalue of the intensity of light energy that reaches the light detector58. When powder is being pumped and flowing through the sensing portion66 of the tube 62, the RMS value calculation will indicate that powderis flowing because this value will fall between the extremes of FIGS. 4Aand 4B.

For either style pump, dense phase or dilute phase, if the output signal64 goes to one of the extremes, then the output signal 64 is indicatingeither a no flow condition (such that the average value would be nearthe maximum voltage output as in FIG. 4A corresponding to no powderpassing through the sensing portion 66); or alternatively anotherproblem such as the hose 16 is obstructed or constricted so that powderis trapped in the sensing portion 66 (such that the average value wouldbe near zero as in FIG. 4B). If the RMS value changes dramatically fromthe initial value, even if not to one of the extremes, then this alsoindicates a potential problem with the pump or the powder flow path.What percentage deviation is used to indicate such a possible situationis a matter of design choice.

The preceding description explains an example of the first configurationto determine or detect flow/no flow conditions. As we previously notedhereinabove, the second configuration allows us to determine whether thepowder flow rate has changed during use of the pump 14. We accomplishthis alternative embodiment, in one example, by including a calibratemode for the response function 54 by which we first determine anexpected average or RMS value for the output signal 64 from the lightdetector 58 for each flow rate setting of interest. These expected orcalibration values may then be used to determine if the actual flow ratehas changed from the desired or programmed flow rate that is set by thepump control 20 and the flow rate control 22 (FIG. 1). FIGS. 4C and 4Dillustrate an example of how this can be done.

Recall that FIG. 4C illustrates the RMS value 74 (V1) for a dense phasepump 14 when the pump is set to 40% of the maximum flow rate. Theaverage value 74 can then be stored as a calibrate value. Suppose nowthat the flow rate changes during a coating operation from 40% to 20% asrepresented in FIG. 4D. FIG. 4D illustrates that at 20% flow rate theRMS voltage output V2 (shown by the time based line 76) from the lightdetector 58 increases owing to the fact that there is less powderflowing through the sensing portion 66 of the tube. Thus, V2>V1. Theresponse function 54 may be programmed so as to detect when the RMS flowrate changes more than, for example, a percentage deviation from thedesired flow rate by calculating when the actual flow rate representedby the RMS output voltage V2 of the light detector 58 has changed(either higher or lower) from the calibrated value V1 by a predeterminedamount or percent. How far the deviation is allowed to go before analert or warning is issued is a matter of design preference.

FIG. 4E illustrates in the exemplary embodiment that when the flow rateincreases, say to 60% of maximum flow, the RMS value output voltage V3(shown by line 78) from the light detector 58 will decrease because morepowder on average is flowing through the sensing portion 66 of the tube.Thus V3<V2 and V3<V1 and V2>V1. Stated another way, V2>V1>V3 for flowrates of 20%, 40% and 60% respectively.

The change in flow rate may be useful, for example, to detect whether anoperator has changed the flow rate setting of the pump from what itshould be for a particular coating recipe, or if the pump operationsomehow has changed the flow rate.

How the calibrate function is carried out is a matter of design choiceand convenience. Different calibrate values may be stored for eachselectable flow rate of the pump, or alternatively the expected orcalibrate value may be determined by simply running the pump 14 at theprogrammed flow rate and storing the detected average or RMS value ofthe detector output 64. This approach however may leave thedetermination susceptible to changes over time of the intensity of thelight generated by the light source 56, the sensitivity of the lightdetector 58, or the transparency of the sensing portion 66 of the tube.Thus, the calibrate mode preferably will be carried out when the systemcomponents are known to be accurate.

The calibrate mode may be run independent of knowing the actual flowrate produced by the pump 14. For example, suppose we want to calibratethe sensing function 52 for the pump 14 at 40% flow rate. We can set theflow rate at 40% and then store the average or RMS value of the lightdetector output 64 as corresponding to whatever the actual powder flowrate from the pump 14 is, whether it is precisely 40% or not we will beable to detect when that flow rate changes. Therefore, we are not inpractice measuring an actual flow rate, but rather analyzing whether theflow rate has changed.

The calibrate mode is also important because different powder materialsmay and typically will have different optical properties such asabsorption, reflectance, translucence and so on. With reference to FIG.4C again, the reference value V1 may indeed change based on the type ofmaterial that is being pumped. Therefore, running a calibrate mode maybe very useful in order to determine the average intensity of lighttransmitted through the sensing portion 66 at a selected flow rate.Alternatively, the system may be calibrated in advance for a variety ofmaterials and flow rates and the average values stored in memory to beaccessed as the calibration value. Many other ways will be apparent toutilize the calibration feature. The calibrate mode therefore may beuseful for both the flow/no flow configuration or the flow rateconfiguration because even for the flow/no flow configuration theaverage value of the detected light intensity may vary based on thepowder material.

Those skilled in the art will readily appreciate that the flow/no flowor first configuration may be used as a special case of the secondconfiguration. For example, if the pump 14 is set at 40% and we have acalibrated RMS value of the light detector 58 output 64 as V1, then ifthe RMS value of the light detector output 64 is noted to approach themaximum value 68 then we have a no flow or low flow condition. The noflow condition may be ascertained different ways, for example, bydetecting when the average or RMS value increases a predeterminedpercentage above the calibrated value V1, or if the average or RMS valuecomes within a predetermined percentage of the maximum value 68. Manyother options are available to the designer to thus determine low flowand no flow conditions.

FIG. 3 illustrates an embodiment of the response function 54. In thisexample, the response function 54 may be realized with a control circuit80, such as for example, a digital processor such as, for example, amicroprocessor 80. A suitable microprocessor is model PIC 16F887available from Microchip. The control circuit 80 receives as an inputthe light detector 58 output signal 64. The control circuit 80 must alsoknow when to monitor the light detector output signal 64 so as not tocreate a false alarm when the pump 14 is not operational. Therefore, thecontrol circuit 80 also may receive a trigger signal 82 as an input fromthe pump control 20. The control circuit 80 can easily and quicklycalculate the average or RMS values of the light detector 58 outputsignal over the time sampling rate is desired. The control circuit 80may light a POWER (PWR) lamp 84 to indicate that system powder to thecontrol circuit 80 is on, as well as light a TRIGGER lamp 86 to indicatethat the pump 14 is active and that the control circuit 80 is monitoringthe light detector output signal 64.

In the first configuration, if the control circuit 80 detects a no flowcondition the control circuit 80 may light a WARNING lamp 88 or activatean audible warning for example. If the no flow condition persists thecontrol circuit 80 may light an ALARM lamp 90.

In the second configuration, the control circuit 80 may light theWARNING lamp 88 if the flow rate changes by a predetermined amount, andthen light the ALARM lamp 90 if the flow rate changes even more or if ano flow condition is detected. These are but a few examples of the manyoptions available as to what to do in response to a detected anomalysuch as with a no flow condition or a change in flow rate. Stillfurther, the control circuit 80 might actuate a relay 92. Change in therelay 92 state may be used to indicate to another control system, suchas for example the control system for the coating line, that there is afault in the powder flow so that the coating system could either beshutdown or at least analyzed to determine if work pieces are beingcoated incorrectly.

Although we use average or RMS values to analyze the light detectoroutput signal 64, such is not required. Many other analytical processesmay be used either on the real time analog output signal from the lightdetector 58 or alternatively a digitized version thereof. As notedbefore, the light detector 58 output contains the information whetherthere is a no flow condition or alternatively a flow rate changecondition. The signal processing may be selected as a matter of designpreference as to how to extract that information and in what form to useit or present it to an operator.

FIGS. 5-7 illustrate an embodiment of one or more of the presentinventions used in an exemplary manner with an exemplary dense phasepump 14. Preferably, the sensing function 52 is disposed near orproximate the outlet 26 of the pump 14. In this embodiment, the pump 14may be an HDLV pump available from Nordson Corporation, Westlake, Ohio.This pump 14 produces pulses or slugs of powder flow through the outlet26. Powder coating material is drawn into the pump 14 via the supplyhose 28 that is in fluid communication with a supply 12 of the powdercoating material. The outlet 26 usually is connected directly with thefeed hose 16, but in this embodiment of the inventions, we install thesensing function 52 in line with the feed hose 16. Thus, is thisexemplary form, an apparatus for detecting powder flow in a tube orpassageway includes the sensing function 52 and the response function54. The response function 54 may be realized in the form describedherein with respect to FIG. 3 or may take on a different embodiment. Thesensing function 52 may be realized in the form described herein withrespect to FIG. 2 or may take on a different embodiment. Note that thecontrol valves 30, 32, 38 and 40 of FIG. 1 along with the flow ratecontrol 22 are incorporated into the pump 14.

The pump 14 may include a main housing 100 that encloses a series of airport controls, valves, pump chambers and fluid passageways that comprisethe pump 14. The pump 14 may operate in accordance with the patentsnoted hereinabove or may be a different design.

The sensing function 52 may be mechanically coupled to the pump 14 inany number of ways. In the embodiment herein, the sensing function 52,which basically includes the light source 56 and the light detector 58(FIG. 7), is disposed on a circuit board or substrate 102. The circuitboard 102 may be U-shaped with the light source 56 on one leg 102 a ofthe U and the light detector 58 on the opposite leg 102 b of the U andfacing each other as in FIG. 7. The recess formed by the U shapereceives a tubular member 104 such that the light source 56 and lightdetector 58 are preferably aligned diametrically opposite each other onopposite sides of the tubular member 104. The tubular member 104 ispreferably transparent to the wavelength(s) of the light energy that istransmitted from the light source 56 to be detected by the lightdetector 58, at least in the region that light energy will pass throughthe tubular member between the light source and light detector.Therefore, the portion 104 through which light energy is transmittedcorresponds to the sensing portion 66 noted in the discussion of FIGS. 1and 2. The circuit board 102 is mounted in a housing 106. The housing106 is illustrated (see FIG. 5) as transparent for convenience ofillustration, but need not be transparent in practice. Portions of thehousing 106 may be transparent as needed without making the entirehousing transparent.

First and second connectors 108, 110 may be used to mount the housing106 near the outlet 26 of the pump 14. The upper or first connector 108comprises an upper portion of the housing 106 and may be coupled as witha snap ring 112 to a first threaded nut 114 that mates with a threadedoutlet member 116 that may include a connector tube piece 116 a from thepump 14 (note in FIG. 7 the outlet member 116 is omitted). This allowsthe entire sensing function 52 assembly to be installed with and removedfrom the pump 14 in a conveniently modular fashion. Thus, the sensingfunction 52 may be an add-on feature for a pump 14 already in the field.When the upper connector 108 is joined to the outlet 26 of the pump 14,the outlet 26 is in fluid communication with the tubular member 104 andpowder will flow through the tubular member 104 out to the feed hose 16.Note that the tubular member 104 is preferably mounted with a verticalorientation and is sufficiently vertical so that gravity may assist inclearing powder through the tubular member 104.

The lower or second connector 110 comprises a lower portion of thehousing 106 and may be used to join the feed hose 16 to the base 106 sothat the feed hose 16 is in fluid communication with the tubular member104. This may be done, for example, with a second threaded nut 118 thatmates to a threaded end of the second connector 110.

An electrical connector 126 may be used to couple a signal cable 128(FIG. 5) to the sensing function 52 so as to provide power to the lightsource 56 and to receive the output from the light detector 58. Thesignal cable 128 is connected at its second end to the response function54 so as to provide the light detector 58 output to the control circuit80 (FIG. 1).

It will be noted that we preferably outwardly flare the tubular member104 at either end 120 a, 120 b. First and second joint members 122, 124are respectively used on each end of the tubular member 104 to form afluid communication between the pump outlet 26 and the tubular member104 and the tubular member 104 to the feed hose 16. The flared entry andexit ends of the tubular member 104 help assure that there are noentrapment areas where the light energy is being transmitted into thetubular member, such that could retain powder which might interfere withinterpreting the signal from the light detector 58.

Therefore, the tubular member 104 that comprises the sensing portion 66may form part of the powder flow path 130 (FIG. 1) from the pump outlet26 to the end use 18 so that the sensing function 52 can be used todetect a flow/no flow condition or alternatively a flow rate changecondition. The tubular member 104 thus provides a sensing portion 66 ofa tube or passageway along the powder flow path 130 through which powderflow is to be detected. But those skilled in the art will appreciatethat if the feed hose 16 is sufficiently transparent in the range ofwavelengths used for the light source 56 and light detector 58, then thesensing function 52 could be mounted directly about the feed hose 16 andthe feed hose itself present the sensing portion 66. Regardless of wherethe sensing function 52 is disposed, the light source 56 and lightdetector 58 will operate with light energy that is directed into thesensing portion of a passageway or tubular member, with the intensity ofthe light energy that passes through to the light detector 58 being afunction of whether powder is flowing through the sensing portion.

Although the exemplary embodiments herein utilize a single light sourceand light detector as the sensing function 52, those skilled in the artwill readily appreciate that additional pairs of sensors may be used.The use of additional pairs may improve overall accuracy of the sensingfunction. For example, a dense phase powder flow pattern within the feedhose 16 or other portion of the powder flow path 130 may form or flow ina rope like pattern that can swirl. This can result in the sensingportion of the powder flow path not being filled with powder even undernormal operating conditions. FIGS. 2 and 2A illustrate an embodiment ofusing two pairs of sensors for the sensing function 52, although evenmore pairs may be used as needed. The second pair 150 is illustrated inFIG. 2 in phantom as it is optional. In this embodiment, the second pair156 (including source 156 and detector 158) may be rotationally offsetfrom the first pair 56, 58. In this example the rotational offset may beninety degrees. If additional pairs are alternatively used, they mayalso be spaced rotationally about the sensing portion of the powder flowpath as needed. By using additional light source/detector pairs, forexample the additional pair 150 positioned ninety degrees rotationallyfrom the first pair 56, 58 we can increase the opportunity to detect thepowder flow. Even more light source/detector pairs may be used, forexample, evenly (or unevenly as may be needed) spaced in a radial mannerabout the sensing portion 104. Whether the detected intensity for eachlight source/detector pair is analyzed separately or processed incombination is a matter of design choice. Furthermore, the one or moreadditional sensing functions 52 may be located elsewhere along thepowder flow path 130 as needed. For example, the second pair 150 isillustrated as not only rotationally offset from the first pair 52, butalso axially offset or spaced from the first pair. However, the pairsmay also be positioned to sense flow through the same sensing portion ofthe powder flow path if required.

In addition to the various apparatus for detecting flow rate of powdercoating material in a tube presented herein, our inventions also includerelated methods of use of the apparatus, as well as a method fordetecting powder flow rate. In an exemplary method, light energy isdirected into a portion of a passageway for powder flow, intensity oflight energy that passes through the passageway is detected, and adetermination of whether powder is flowing in the passageway is madebased on the detected intensity. In one embodiment, the method includesdetermining an average or RMS value of the intensity of the light energythat passes through the passageway. In another embodiment, the detectedintensity of the light energy, for example the average or RMS value, iscompared to a calibrated value to determine if the powder flow rate haschanged.

We thus provide method and apparatus for detecting or verifying thepresence or transport of airborne solid particles in a passageway ortube. We accomplish this detection in a manner without introducing adisturbance in the powder flow, or in other words with a non-invasivetechnique. For example, we accomplish the detection without changing thefluid passage cross-sectional area, without introducing additional airflow, without creating a pressure change or without creating aninterruption or change in flow direction. The powder flow path from thepump outlet to the end use is thus not changed as to the operationalaspects including pressure, flow rate or direction, temperature and soon.

It is intended that the inventions not be limited to the particularembodiments disclosed for carrying out the inventions, but that theinventions will include all embodiments falling within the scope of theappended claims.

We claim:
 1. Apparatus for detecting pulsed powder flow in a tube,comprising: a powder pump comprising a pump chamber wherein powder isdrawn into said pump chamber by negative pressure applied to said pumpchamber and powder is pushed out of said pump chamber when positivepressure is applied to said pump chamber, said powder flowing in pulsesfrom said pump chamber into a powder flow path, a light source, a lightdetector for detecting light from said light source when said lightsource produces light that passes into a portion of said powder flowpath, said light detector producing an output in response to the lightfrom said light source that passes through said portion of said powderflow path, a circuit that receives said output and determines whetherpowder is flowing through said portion of said powder flow path based onsaid output, wherein a first valve controls the flow of powder into saidpump chamber and a second valve controls the flow of powder out of saidpump chamber.
 2. The apparatus of claim 1 wherein said powder pumpcomprises two pump chambers that alternately supply powder to saidpowder flow path.
 3. The apparatus of claim 1 wherein said powder pumpfurther comprises a controller that includes said circuit.
 4. Theapparatus of claim 1 wherein said light detector output is pulsed andsaid circuit that receives said pulsed output from said light detectordetermines an average of said intensity of light received by said lightdetector.
 5. The apparatus of claim 1 wherein said light source and saidlight detector are disposed on diametrically opposite sides of saidportion of said powder flow path.
 6. The apparatus of claim 1 whereinsaid portion of said powder flow path is light transparent.
 7. Theapparatus of claim 1 wherein said portion of said powder flow path istransparent to wavelengths of light produced by said light source andthat can be detected by said light detector.
 8. The apparatus of claim 1wherein said portion of said powder flow path is oriented so thatgravity assists powder flowing through said portion of said powder flowpath.
 9. The apparatus of claim 8 wherein said portion of said powderflow path is vertically oriented.
 10. The apparatus of claim 1 whereinsaid light detector produces said output as a voltage signal, saidcircuit determining an RMS value of said voltage signal.
 11. Theapparatus of claim 10 wherein said light detector output is pulsed andsaid circuit determines RMS value of said output of said light detectorincluding a no flow RMS value when powder is not flowing through saidportion of said powder flow path, said circuit determining that powderis flowing through said portion of said powder flow path when an RMSvalue of said output of said light detector is different from said noflow RMS value.
 12. The apparatus of claim 11 wherein said circuitdetermines said no flow RMS value based on a maximum signal produced bysaid light detector when no powder is flowing through said portion ofsaid powder flow path, so that powder flowing through said portion ofsaid powder flow path reduces intensity of light received by said lightdetector and reduces an RMS value of said output to indicate powder isflowing through said portion of said powder flow path.
 13. The apparatusof claim 1 wherein said light detector output is pulsed and said circuitdetermines a first RMS value of said output of said light detector for afirst powder flow rate through said portion of said powder flow path anddetermines that flow rate has changed when a second RMS value of saidoutput from said light detector is different from said first RMS valueby a selected amount.
 14. The apparatus of claim 1 wherein said circuitgenerates an alarm when said circuit determines that powder is notflowing through said portion of said powder flow path.
 15. The apparatusof claim 14 wherein said alarm comprises a visual alarm or an audiblealarm or both.
 16. The apparatus of claim 1 wherein said portion of saidpowder flow path has a sufficient length to diameter ratio so that anypowder that may collect at a boundary layer of said portion of saidpowder flow path does not affect light that is transmitted into saidportion of said powder flow path by said light source that wouldotherwise be received by said light detector.
 17. The apparatus of claim1 comprising two or more light sources or light detectors or both. 18.The apparatus of claim 17 comprising a first light source/detector pairand a second light source/detector pair, wherein said first pair isrotationally offset from said second pair.
 19. The apparatus of claim 18wherein said first pair is offset axially and rotationally from saidsecond pair.
 20. The apparatus of claim 1 wherein said light source andsaid light detector are contained in a housing that is located alongsaid powder flow path.
 21. The apparatus of claim 20 wherein saidhousing is attached to a tubular member.
 22. The apparatus of claim 21wherein said tubular member is a powder feed hose.
 23. The apparatus ofclaim 20 wherein said housing is transparent.
 24. The apparatus of claim1 wherein said light source and said light detector are located alongsaid powder feed path between said pump chamber and a spray gun.
 25. Theapparatus of claim 1 wherein said pump chamber comprises a cylindricalgas permeable filter member.
 26. The apparatus of claim 1 wherein saidfirst valve and said second valve each comprise a pinch valve.
 27. Theapparatus of claim 1 wherein each pinch valve opens and closes inresponse to pneumatic pressure on a flexible valve body.
 28. Powdercoating system, comprising: a powder pump comprising a pump chamberwherein powder is drawn into said pump chamber by negative pressureapplied to said pump chamber and powder is pushed out of said pumpchamber when positive pressure is applied to said pump chamber, saidpowder flowing in pulses from said pump chamber into a powder flow path,a first valve to control the flow of powder into said pump chamber and asecond valve to control the flow of powder out of said pump chamber, asupply of powder coating material to supply powder coating material tosaid powder pump through a supply hose, said powder pump being operableto supply powder coating material through a feed hose to a spray gun, alight source, a light detector for detecting light from said lightsource when said light source produces light that passes into a portionof said powder flow path, said light detector producing an output inresponse to the light from said light source that passes through saidportion of said powder flow path, a control circuit that receives saidoutput and determines whether powder is flowing through said portion ofsaid powder flow path based on said output.
 29. The powder coatingsystem of claim 28 wherein said control circuit produces a controlcircuit output based on whether powder is flowing through said portionof said powder flow path.
 30. The powder coating system of claim 29wherein said control circuit output comprises activating a warning oralarm.
 31. The powder coating system of claim 29 wherein said controlcircuit output is used to control operation of the powder coatingsystem.
 32. The powder coating system of claim 28 wherein said controlcircuit produces a control circuit output that is based on flow rate ofpowder coating material through said powder flow path.